This project aims to identify dietary determinants of benign breast disease (BBD) using data on childhood, adolescent, and adult diet. Evaluating determinants of proliferative benign breast disease has several important advantages. First we can examine an earlier stage in the disease process and second, identifying parallel effects of an exposure for breast cancer as well as for a precursor lesion (proliferative disease with atypia), would support a causal interpretation. We will build on the unique resource of NHSII, a cohort of young adults who provided dietary data in 1991, to assess relations between diet and incidence of BBD through 1997. Additional follow-up will permit refinement of preliminary results which show that age at menarche is strongly inversely related to risk of proliferative changes on breast biopsy, that dietary fat is associated with increased risk, and folate and vitamin C intakes are associated with decreased risk. Specifically we hypothesize that higher total fat and saturated fat intake in both adult and adolescent diet is associated with increased incidence of proliferative BBD; increased alcohol intake in adult life is associated with increased risk of proliferative BBD; that higher intakes of dietary vitamin A, carotenoids, vitamins E and C, during adolescence and adulthood are associated with decreased risk,; and that in utero exposures reflected in birth weight and galactorrhea are associated with increased risk of proliferative BBD. Centralized pathology review using established criteria for proliferative disease and for atypia will ensure that the outcome for this study is uniformly defined and reproducible. Through 1997 we expect to identify and complete histopathology review for 1539 incident cases of BBD. This study offers a unique opportunity to examine prospectively diet in relation to early stages of breast cancer. Further, this can be conducted efficiently within the ongoing NHSII cohort which provides the exposure and follow-up information, and because of the study's integration into the program project provides resources and expertise developed by the research group over the last 15 years.